Reclosers, also known as autoreclosers, are used in electric power distribution systems or networks. A recloser functions like a circuit breaker, but with the ability to automatically close the breaker after the breaker has been opened due to a fault in supplying or distributing power, for example, when one or more power distribution lines connected to the recloser are short circuited. Some faults are only momentary, such as a falling tree branch hitting a power distribution line. Without a recloser, a fault causing the breaker to open will require a manual reset. This is time consuming, and will cause wide-spread inconvenience due to power failure. A recloser allows automatic closing of the breaker after the breaker is opened. This is to test whether the fault is momentary. For example, during a thunderstorm, if lightning were to strike the distribution system, the power to one's home may be disrupted for a few seconds causing lights and appliances to turn OFF (recloser opening), then ON (recloser closing). Once the recloser closes, if it senses the continued presence of increased current, it will again open. Such cycling between open and closed may occur a few times, usually three times, before the recloser remains open. These sequences of operation are called “reclose sequences”.
During “reclose sequences”, the recloser must be able to open very quickly after closing (usually less than 73 ms (time required for the DC component of the fault current to drop to 20% of its initial value), in order to comply with standard IEC 62271-100.
Reclosers are usually mounted to the poles or towers which suspend power lines above the ground. Use of reclosers in underground systems is also known.